You need to submit the I-751 and evidence showing that the marriage was entered in good faith. They are interested in evidence during the last two years since you got your GC.
Seeing that you live in CT, you will need to submit your I-751, check, and evidence to the Vermont Service Center in St. Albans, VT. Shortly after you submit your paperwork, you will receive a receipt that serves as a one-year extension for your GC. With this letter and your GC you are still allowed to work and travel. My wife has traveled at least twice internationally with this letter and GC with no issues. About a week or so after getting the letter you will get a appointment notice to appear at ASC to be fingerprinted and have your picture taken. Then the waiting game begins. We filed the paperwork in early Jan for a March card expiration date and still haven't heard on the status of the case. Based on my calculations we should be hearing any day now. Also, for some reason, the receipt number on the extension letter and the ASC appointment notice are different, however, the one on the ASC appointment notice is the one that you need in order to check your status online.